feat(core/core-rest-pipeline): migrate to #platform/* imports

[deyaaeldeen]

Migrate @azure/core-rest-pipeline to #platform/* conditional imports:

• #platform/userAgent — platform-specific user agent string generation
• #platform/wrapAbortSignal — React Native AbortSignal compatibility shim
• #platform/createFile — platform-specific File creation (Node raw content vs browser native)
• Replace NodeJS.ReadableStream/Buffer/ReadableStream with NodeReadableStream/NodeBuffer/WebReadableStream from @typespec/ts-http-runtime
• Per-platform tsconfigs under config/, updated eslint/vitest/warp configs

[Copilot]

Pull request overview

This PR migrates @azure/core-rest-pipeline to internal #platform/* conditional imports to provide per-runtime implementations (browser / react-native / node) while keeping a unified public API surface.

Changes:

• Introduce #platform/* conditional imports for user agent generation, AbortSignal wrapping, and File creation (with package.json imports mappings).
• Replace Node/browser stream & buffer types with NodeReadableStream/NodeBuffer/WebReadableStream from @typespec/ts-http-runtime and update API reports accordingly.
• Restructure build/test configuration to use per-platform tsconfigs under config/, align eslint/vitest configs, and add a react-native Vitest config entrypoint + test script.

Reviewed changes

Copilot reviewed 33 out of 34 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
sdk/core/core-rest-pipeline/warp.config.yml	Points warp targets at per-platform tsconfigs under ./config/.
sdk/core/core-rest-pipeline/vitest.react-native.config.ts	Adds RN Vitest config re-export from eng/vitestconfigs.
sdk/core/core-rest-pipeline/vitest.browser.config.ts	Switches browser Vitest config to eng/vitestconfigs/browser.config.ts.
sdk/core/core-rest-pipeline/tsconfig.json	Updates project references to the new config/ tsconfigs.
sdk/core/core-rest-pipeline/tsconfig.test.node.json	Removed in favor of config/tsconfig.test.node.json.
sdk/core/core-rest-pipeline/tsconfig.test.json	Removed in favor of explicit config/ references.
sdk/core/core-rest-pipeline/tsconfig.src.json	Removed in favor of per-platform config/tsconfig.src.*.json.
sdk/core/core-rest-pipeline/tsconfig.snippets.json	Removed in favor of config/tsconfig.snippets.json.
sdk/core/core-rest-pipeline/tsconfig.samples.json	Removed in favor of config/tsconfig.samples.json.
sdk/core/core-rest-pipeline/tsconfig.browser.config.json	Removed in favor of config/tsconfig.test.browser.json.
sdk/core/core-rest-pipeline/test/util.ts	Uses @azure/core-util stringToUint8Array when collecting stream chunks.
sdk/core/core-rest-pipeline/test/internal/node/userAgentPlatform.spec.ts	Removes the “empty process.versions” test case.
sdk/core/core-rest-pipeline/test/internal/formDataPolicy.spec.ts	Adjusts arrayBuffer() access typing to avoid relying on Blob narrowing.
sdk/core/core-rest-pipeline/test/internal/browser/userAgentPlatform.spec.ts	Updates to import platform impl via #platform/userAgent and adds header-name assertion.
sdk/core/core-rest-pipeline/src/util/wrapAbortSignal-rn.mts	Adds RN-specific AbortSignal shim implementation.
sdk/core/core-rest-pipeline/src/util/userAgentPlatform.ts	Updates Node platform detection typing via global augmentation of NodeJS.ProcessVersions.
sdk/core/core-rest-pipeline/src/util/userAgentPlatform-browser.mts	Refactors browser user agent data typing and Edge runtime handling.
sdk/core/core-rest-pipeline/src/util/userAgent.ts	Switches to #platform/userAgent conditional import.
sdk/core/core-rest-pipeline/src/util/react-native.d.ts	Removes custom react-native module typing (now relying on RN types).
sdk/core/core-rest-pipeline/src/util/file.ts	Migrates stream/buffer types to ts-http-runtime aliases; adds createRawFile; routes createFile via #platform/createFile.
sdk/core/core-rest-pipeline/src/util/createFile.ts	Adds Node/default createFile implementation via createRawFile.
sdk/core/core-rest-pipeline/src/util/createFile-browser.mts	Adds browser/RN createFile implementation using native File.
sdk/core/core-rest-pipeline/src/policies/wrapAbortSignalLikePolicy.ts	Switches to #platform/wrapAbortSignal import.
sdk/core/core-rest-pipeline/src/interfaces.ts	Replaces Buffer/NodeJS.ReadableStream/ReadableStream types with ts-http-runtime aliases.
sdk/core/core-rest-pipeline/src/index.ts	Removes DOM stubs and re-exports ts-http-runtime stream/buffer types.
sdk/core/core-rest-pipeline/src/defaultHttpClient.ts	Switches to #platform/wrapAbortSignal import.
sdk/core/core-rest-pipeline/review/core-rest-pipeline-react-native.api.diff.md	Captures RN API diffs vs node baseline.
sdk/core/core-rest-pipeline/review/core-rest-pipeline-node.api.md	Updates node API report for new stream/buffer types and re-exports.
sdk/core/core-rest-pipeline/package.json	Adds imports mappings for #platform/*; updates scripts to use new config/ tsconfigs and adds RN test run.
sdk/core/core-rest-pipeline/eslint.config.mjs	Aligns eslint config shape with other core packages; points parser project to ./config/tsconfig.lint.json.
sdk/core/core-rest-pipeline/config/tsconfig.*.json	Adds per-platform src/test/samples/snippets/lint tsconfigs extending eng/tsconfigs.